This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2000-036708, filed Feb. 15, 2000; and No. 2000-046232, filed Feb. 23, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates to a press forming machine for optical devices which manufactures a glass optical device such as a lens, prism, and optical communication component by press forming.
FIG. 5 is a schematic view showing the structure of a conventional press forming machine for optical devices disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-186230.
A fixed shaft 2 extends downward from the upper portion of a frame 1, and an upper die unit 4 is attached to the lower end face of the shaft 2 with a heat insulating block 3 made of a ceramic material. The upper die unit 4 is comprised of a die plate made of metal 5, an upper die 6 made of ceramic (or sintered hard alloy), and a fixed die 7. The fixed die 7 fixes the upper die 6 to the die plate 5 and forms part of a die.
A driving unit 8 (a screw jack in this example) is provided to the lower portion of the frame 1. The driving unit 8 has a servo motor 8a as a driving source and converts rotation of the servo motor 8a into a thrust of linear motion. A moving shaft 9 is attached to the distal end of the driving shaft of the driving unit 8 with a load cell 8b. The moving shaft 9 extends upward to oppose the fixed shaft 2. The speed, position, and axial load of the moving shaft 9 are controlled by a program input to a controller 28, so the moving shaft 9 can move in the vertical direction.
A lower die unit 11 is attached to the upper end face of the moving shaft 9 with a ceramic heat insulating block 10. The lower die unit 11 is comprised of a die plate 12 made of metal, a lower die 13 made of ceramic (or sintered hard alloy), and a moving die 14. The moving die 14 fixes the lower die 13 to the die plate 12 and forms part of a die.
The fixed shaft 2 extends through an opening formed at the central portion of an upper plate 15. The upper plate 15 is driven in the vertical direction by a driving unit (not shown). An O-ring is fitted in the opening of the upper plate 15, and the upper plate 15 can slide in the vertical direction with a portion between it and the outer surface of the fixed shaft 2 being kept airtight.
The moving shaft 9 extends through an opening formed at the central portion of a lower plate 1a. The lower plate 1a is fixed to the frame 1. An O-ring is fitted in the opening of the lower plate 1a, and the moving shaft 9 can slide in the vertical direction with a portion between it and the inner surface of the lower plate 1a being kept airtight.
The upper and lower die units 4 and 11 which form a pair, the heat insulating blocks 3 and 10, the lower end of the fixed shaft 2, and the upper end of the moving shaft 9 are surrounded by a cylindrical member made of silica glass (transparent quartz tube 16). The upper end face of the transparent quartz tube 16 abuts against the lower surface of the upper plate 15, and an O-ring is mounted in that portion of the upper plate 15 which comes into contact with the transparent quartz tube 16 to maintain airtightness. Similarly, the lower end face of the transparent quartz tube 16 abuts against the upper surface of the lower plate 1a, and an O-ring is mounted in that portion of the lower plate 1a which comes into contact with the transparent quartz tube 16 to maintain airtightness. Hence, a forming chamber 17 which is airtight against the outside is formed inside the transparent quartz tube 16.
An outer tube 18 is arranged to surround the transparent quartz tube 16. The upper end of the outer tube 18 is connected to the outer surface of the upper plate 15, and the lower end of the outer tube 18 is in contact with the upper surface of the lower plate 1a. A lamp unit 19 is mounted at the middle stage of the outer tube 18. The upper and lower die units 4 and 11 located inside the transparent quartz tube 16 are heated by radiation from the lamp unit 19. The lamp unit 19 is comprised of infrared lamps 20, a reflecting mirror 21 arranged behind the infrared lamps 20, a water-cooled pipe 22 for cooling the reflecting mirror 21. Both the infrared lamps 20 and reflecting mirror 21 are formed by stacking in a plurality of stages ring-like components each constituted by mating two semicircular arcuate elements, to form a cylindrical shape as a whole.
The fixed shaft 2, moving shaft 9, and upper plate 15 respectively have gas supply paths 23, 24, and 25. The lower plate 1a has an exhaust port 26. An inert gas is supplied into the forming chamber 17 at a predetermined flow rate through the gas supply paths 23, 24, and 25, and is discharged through the exhaust port 26, to maintain the interior of the forming chamber 17 in an inert gas atmosphere and to cool the upper and lower die units 4 and 11.
A thermocouple 27 is attached to the rear surface of the die plate 12. The thermocouple 27 detects the temperature of the lower die unit 11.
When manufacturing an optical device of ordinary optical glass (with a glass transition point of 800xc2x0 C. or less), press forming is performed at a temperature of about 800xc2x0 C. by using the machine as shown in FIG. 5.
For example, a stepper lens used in a semiconductor manufacturing process requires a high ultraviolet transmittance, and accordingly silica glass is used to form it. In a V-groove board used for an optical communication V-groove connector, silica glass is used so that the thermal expansion coefficient of the optical communication V-groove connector coincides with that of a silica glass optical fiber and optical waveguide. This silica glass optical device is conventionally manufactured by grinding and polishing processes. Therefore, to manufacture such an optical device requires a long period of time and high cost.
If such a silica glass optical component is to be manufactured by press forming in order to reduce the manufacturing cost, as the silica glass has a high glass transition point and a high forming temperature of about 1,300xc2x0 C. to 1,600xc2x0 C., the following various problems arise in the performance of the machine at elevated temperature.
(a) Since the temperature of the transparent quartz tube 16 increases, the transparent quartz tube 16 may deform, the seal packings in contact with the two ends of the transparent quartz tube 16 may be damaged, and a reaction product may attach to the inner and outer surfaces of the transparent quartz tube 16.
(b) Since the temperature of the quartz bulbs surrounding the filaments of the infrared lamps 20 increases, the quartz bulbs deform.
(c) Since the temperature of the reflecting mirror 21 arranged behind the infrared lamps 20 increases, the reflecting coating film (e.g., gilt finish film) applied to the reflecting surface peeks off.
(d) Since the temperature of the terminal portions of the infrared lamps 20 increases to 300xc2x0 C. or more, the molybdenum foils and pins of the sealing portions of the terminals of the infrared lamps 20 are oxidized. This shortens the service life of the infrared lamps 20.
Furthermore, to increase the forming temperature to 1,000xc2x0 C. or more is not easy with the conventional forming machine due to the following reason.
In the conventional press forming machine for optical devices, as shown in FIG. 5, the lamp unit 19 is arranged outside the transparent quartz tube 16 to surround the pair of upper and lower die units 4 and 11. The pair of upper and lower die units 4 and 11 and a preform 30 are heated by infrared rays radiated from the lamp unit 19. Since most of the infrared rays are transmitted through the preform 30 made of silica glass, the preform 30 is mainly heated by the heat conduction from the upper and lower dies 6 and 13 and from the ambient gas in the forming chamber 17. Therefore, the output from the lamp unit 19 must be increased larger than in the conventional case. Also, the temperature of the ambient gas in the forming chamber 17 must be increased to a value near a forming temperature. The conventional forming machine, however, does not have sufficiently high heat insulating properties for the interior of the forming chamber, and it is accordingly not easy to increase the temperature of the ambient gas in the forming chamber to 1,000xc2x0 C. or more.
The present invention has been made in view of the problems of the conventional press forming machine for optical devices as described above. It is the first object of the present invention to provide a press forming machine for optical devices which does not cause damage to components constituting the machine even when the forming temperature is set to 1,000xc2x0 C. or more and can accordingly be used for press-forming a material with a high glass transition point such as silica glass. It is the second object of the present invention to provide a press forming machine for optical devices which has excellent heat insulating properties for the interior of the forming chamber and allows the temperature of the atmospheric gas in the forming chamber to reach a value near the glass transition point of silica glass within a short period of time.
According to the present invention, there is provided a press forming machine for optical devices, which heats a material to be formed and thereafter forms the material, thereby manufacturing an optical device, comprising:
a pair of upper and lower press dies for forming the material;
a pair of upper and lower shafts for respectively supporting the press dies from behind;
a cylindrical member surrounding the pair of press dies and distal ends of the shafts to form an airtight chamber therein, the cylindrical member being made of a material transparent to infrared rays;
infrared lamps arranged along an outer surface of the cylindrical member to surround the pair of press dies;
a reflecting mirror arranged behind the infrared lamps to form a cylindrical shape as a whole; and
a jacket attached to cover a rear surface of the reflecting mirror and supplied with a cooling gas,
wherein the reflecting mirror has a plurality of through holes through which the cooling gas is sprayed from the jacket toward the outer surface of the cylindrical member.
With the press forming machine for optical devices according to the present invention, the reflecting mirror, infrared lamps (more specifically, quartz bulbs for housing filaments), and cylindrical member are cooled by spraying the cooling gas from the rear surface of the reflecting mirror, so that a temperature increase in these constituent components is suppressed. Even when the press forming temperature is set to 1,000xc2x0 C. or more, these constituent components can be prevented from deforming or being damaged. As a result, an optical component can be manufactured from silica glass with a high glass transition point by press forming.
Preferably, the cooling gas sprayed toward the outer surface of the cylindrical member is recovered from both ends of the cylindrical member. The recovered cooled gas is cooled by a heat exchanger, and is discharged outside the machine. Hence, hot gas is prevented from being discharged from the machine, and the atmosphere in a room where the machine is installed can be maintained at a good state.
The cooling gas cooled by the heat exchanger can be circulated in the jacket again. This method is particularly effective, when the machine is installed in a clean room, in order to maintain the atmosphere in the clean room. This method is also effective when a gas other than air, e.g., an inert gas, is used as the cooling gas.
Preferably, a terminal chamber for housing terminal portions of the infrared lamps is provided in the press forming machine for optical devices of the present invention. The cooling gas is supplied into the terminal chamber as well, thereby cooling the terminal portions of the infrared lamps. As a result, damage to the infrared lamps can be prevented, and the service life of the infrared lamps can be prolonged.
According to the present invention, there is also provided a press forming machine for optical devices, which heats a material to be formed and thereafter forms the material, thereby manufacturing an optical device, comprising:
a pair of upper and lower press dies for forming the material;
a pair of upper and lower shafts for respectively supporting the press dies from behind;
a pair of upper and lower heat insulating members inserted between distal end faces of the respective shafts and rear surfaces of the press dies to decrease a heat flux flowing out from the press dies through the shafts;
a cylindrical member surrounding the pair of press dies, the pair of heat insulating members, and distal ends of the shafts to form an airtight chamber therein, the cylindrical member being made of a material transparent to infrared rays;
upper and lower plates respectively connected to upper and lower ends of the cylindrical member and having through holes at central portions thereof through which the shafts extend slidably through seal members;
infrared lamps arranged along an outer surface of the cylindrical member to surround the pair of press dies;
a first reflecting mirror arranged behind the infrared lamps to have a cylindrical shape as a whole;
a second reflecting mirror arranged to surround the cylindrical member and occupying a range extending from an upper end of the first reflecting mirror to a lower surface of the upper plate to form a cylindrical shape as a whole; and
a third reflecting mirror arranged to surround the cylindrical member and occupying a range extending from a lower end of the first reflecting mirror to an upper surface of the lower plate to form a cylindrical shape as a whole.
According to the press forming machine for optical devices of the present invention, since the second and third reflecting mirrors are arranged above and under the first reflecting mirror in the above manner, heat radiated from the vicinities of the distal ends of the pair of upper and lower shafts through the cylindrical member is reflected by the second and third reflecting mirrors to return to the shafts it is radiated from. Thus, heat dissipated outside the forming chamber decreases, so that the heat insulating properties in the forming chamber are improved. As a result, the atmosphere temperature in the forming chamber can increase to reach a value near the glass transition point of silica glass quickly and efficiently.
Other than formation of optical devices, the above method can also be applied to forming or sintering a metal.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.